linux-kernel - [tip: x86/cpu] x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

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Message-ID: <176578311272.498.3625790823072042019.tip-bot2@tip-bot2>
Date: Mon, 15 Dec 2025 07:18:32 -0000
From: "tip-bot2 for Andrew Cooper" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, Ingo Molnar <mingo@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Pu Wen <puwen@...on.cn>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/cpu] x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     0bc03750deefc5fdab77b01c459bb1691c64c3c5
Gitweb:        https://git.kernel.org/tip/0bc03750deefc5fdab77b01c459bb1691c64c3c5
Author:        Andrew Cooper <andrew.cooper3@...rix.com>
AuthorDate:    Wed, 26 Nov 2025 12:51:47 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Sun, 14 Dec 2025 09:57:13 +01:00

x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

Besides formatting changes, this logic dates back to Linux 2.4.0-test11 in
November 2000.

Prior to "Massive cleanup of CPU detection and bug handling",
c->x86_capability was a single u32 containing cpuid(1).edx,
cpuid(0x80000001).edx, or a synthesis thereof.  X86_FEATURE_AMD3D was
defined as the top bit this single u32.

After "Massive cleanup of CPU detection and bug handling",
c->x86_capability became an array with AMD's extended feature leaf split
away from Intel's basic feature leaf.

AMD doc #20734-G states that 3DNow is only enumerated in the extended
feature leaf, and that other vendors where using this bit too.  i.e. AMD
never produced a CPU which set bit 31 in the basic leaf, meaning that
there's nothing to clear out in the first place.

This logic looks like it was relevant in the pre-"Massive cleanup" world
but ought to have been dropped when c->x86_capability was properly split.

Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Pu Wen <puwen@...on.cn>
Link: https://patch.msgid.link/20251126125147.880275-1-andrew.cooper3@citrix.com
---
 arch/x86/kernel/cpu/amd.c     | 6 ------
 arch/x86/kernel/cpu/centaur.c | 6 ------
 arch/x86/kernel/cpu/cyrix.c   | 6 ------
 arch/x86/kernel/cpu/hygon.c   | 6 ------
 4 files changed, 24 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index c04f53f..c792c2a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1051,12 +1051,6 @@ static void init_amd(struct cpuinfo_x86 *c)

 	early_init_amd(c);

-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	if (c->x86 >= 0x10)
 		set_cpu_cap(c, X86_FEATURE_REP_GOOD);

diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
index a3b55db..c839894 100644
--- a/arch/x86/kernel/cpu/centaur.c
+++ b/arch/x86/kernel/cpu/centaur.c
@@ -119,12 +119,6 @@ static void init_centaur(struct cpuinfo_x86 *c)
 	u32  fcr_clr = 0;
 	u32  lo, hi, newlo;
 	u32  aa, bb, cc, dd;
-
-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
 #endif
 	early_init_centaur(c);
 	init_intel_cacheinfo(c);
diff --git a/arch/x86/kernel/cpu/cyrix.c b/arch/x86/kernel/cpu/cyrix.c
index dfec2c6..8f22085 100644
--- a/arch/x86/kernel/cpu/cyrix.c
+++ b/arch/x86/kernel/cpu/cyrix.c
@@ -195,12 +195,6 @@ static void init_cyrix(struct cpuinfo_x86 *c)
 	char *buf = c->x86_model_id;
 	const char *p = NULL;

-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	/* Cyrix used bit 24 in extended (AMD) CPUID for Cyrix MMX extensions */
 	if (test_cpu_cap(c, 1*32+24)) {
 		clear_cpu_cap(c, 1*32+24);
diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index 1fda6c3..7f95a74 100644
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -174,12 +174,6 @@ static void init_hygon(struct cpuinfo_x86 *c)

 	early_init_hygon(c);

-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	set_cpu_cap(c, X86_FEATURE_REP_GOOD);

 	/*